Summary

VPN can take several forms. It can exist between two end systems, or it can exist between two or more networks. A VPN can be built by using tunnels, encryption, or one of the virtual router methods. A VPN can consist of networks that are connected to a service provider’s network by leased lines, Frame Relay or ATM or a VPN can consist of dial-up subscribers that connect to centralized services or other dial-up subscribers.

VPNs are a quite idealistic subject which is there is no single defining product, or even much of a agreement among VPN vendors as to what comprises a VPN. Therefore, everyone knows what a VPN is but establishing a single definition can be remarkably difficult.

Every organization has problems that it must solve, and each of the tools that have been mentioned can be used to construct a certain type of VPN to address a particular set of functional objectives. More than one tool is available to address these problems and network engineers should be aware that VPNs are an area in which many people use the term commonly which is there is a broad problem with many possible solutions. Each solution has numerous strengths, weaknesses and vulnerabilities. No single method exists for VPNs that will replace all others in the months and years to come. Instead, a diversity of technological choices in this area of VPN support will continue to appear.
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